Design Comparison of NdFeB and Ferrite Radial Flux Surface Permanent Magnet Coaxial Magnetic Gears

Magnetic gears promise the benefits of mechanical gears with added advantages from contactless power transfer. Although most of the literature focuses on minimizing the size of magnetic gears, their material costs must also be reduced to achieve economic feasibility. This paper compares the active material costs of NdFeB and ferrite radial flux coaxial magnetic gears with surface permanent magnets through a parametric two-dimensional (2-D) and 3-D finite element analysis study. Differences in optimal design trends such as pole counts and magnet thicknesses are illustrated for the two materials. The results demonstrate that, for most historical price rate scenarios, NdFeB gear designs are capable of achieving lower active material costs than ferrite gear designs, and they are always capable of achieving much higher torque densities. Based on the selected design constraints, relative to a nominal ferrite cost of $10/kg, NdFeB must cost more than $90/kg before ferrite is cost competitive. However, ferrite gears can achieve higher efficiencies than NdFeB gears, especially at high speeds, and generally emit less axial leakage flux. Additionally, contour plots are provided to show the impact of material price rate variation on the cost break points.